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| Home > Publications database > Modelling of High Temperature Polymer Electrolyte Fuel Cells |
| Book/Dissertation / PhD Thesis | FZJ-2017-07858 |
2017
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-263-4
Please use a persistent id in citations: http://hdl.handle.net/2128/16228
Abstract: Fuel cells are energy conversion devices that generate electricity and heat through electrochemical reactions involving hydrogen and oxygen. They are divided into different types according to the electrolytes and the operating temperatures. One promising fuel cell type, which can be used as an on-board power supply in trucks or airplanes, is the high-temperature polymer electrolyte fuel cell (HT-PEFC). In a HTPEFC, phosphoric acid-doped polybenzimidazole is employed in the electrolyte. The typical working temperature of this fuel cell type is between 150 °C and 180 °C. The aim of this thesis is the 3D modeling of HT-PEFC at the cell level, in order to better understand the physical and electrochemical processes within the cell. The open-source software Open FOAM is used as a platform for model development. Four models were implemented to describe different phenomena.• The first model describes electrochemistry with effective parameters related to the geometric surface of the catalyst layer. Mass transfer in the porous gas diffusion layer is represented by a simpleFick’s law approach. • The second model employs a macrohomogeneous approach for the description of electrochemistry, whereby the penetration depth of the electrochemical reaction in the catalyst layer is considered to be a function of the current density. • A mathematical description of water transport from the cathode side to the anode side of the phosphoric acid doped polybenzimidazole membrane, during fuel cell operation, is depicted in thethirdmodel. • The fourth model compares gas transport in the gas diffusion layer, as described by a Stefan-Maxwell approach, with the gas transport according to model 1, above. The mathematical models developed in the present work were validated by comparison of the numericalcalculations with experimental data and analytical solutions. Two different cell geometries were considered: a cell with parallel straight channels, with an active area of 0.2 cm$^{2}$, and a 50 cm$^{2}$ cell, with meandering (serpentine) channels. The results of performance calculations in terms of the distributions of local species, velocity, temperature and current density, under different operating conditions are presented and discussed in detail. The results show the influence of mass transport-inhibition by mechanical compression of the gas diffusion layers under the ribs on the local gas partial pressure, as well as on the current density distribution. Furthermore it is shown that, under the present situation, the description of the diffusion species in the gas diffusion layer, by means of a Maxwell-Stefan formulation, is essentially the same as one by means of the Wilke approach. The macrohomogeneous approach for the description of electrochemistry in the catalyst layer, desrcibed in the second model, results in a more homogeneous current density distribution compared to the surface-oriented approach from model1. The significance of water transport through the membrane from the cathode side to the anode side is also described and discussed. Phosphoric acid concentrations, which are caused by water production and water transport, differ on the anode and cathode sides of the membrane. On the anode-side boundary surface between the membrane and catalyst layer, a 95.3% phosphoric acid concentration is observed. On the cathode side, a value of 93.9% is obtained. These results are in good agreement with experimental data.
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